IEEE 802.21 MEDIA INDEPENDENT HANDOVER
DCN:21-08-0309-02
Title: Responses to 802.21b PAR comments
Date Submitted: November 10, 2008
Presented at IEEE 802.21 session #29 in Dallas, TX
Authors or Source(s): Juan Carlos Zuniga and Burak Simsek
Abstract: Responses to comments received from the different IEEE
802 working groups on the 802.21b PAR and 5C.
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802.16 Comments 1/10
General Comments
• Please explain the user cases. We are stipulating two possible ones below:
• 1) Downlink Only (DOB) to 802.x and 802.x to DOB HO’s may be valid
use cases and possibly can be addressed in IEEE, e.g user A is watching
ESPN in DOB and enters a 802.x coverage while leaving DOB coverage. Is
it for 802.21 to address it? Why?
 Yes. Currently 802.21 supports handovers between 802 and non-802
technologies (i.e. 3GPP and 3GPP2) as well, so 802.21b will amend the
specification to support one more type of non-802 technology.
 The DVB Project is starting a Work Item to look at how 802.21 can be used
to enhance these handovers and are planning to have a direct liaison with
802.21 to inform about the status of this Work Item.
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802.16 Comments 2/10
General Comments
• Please explain the user cases. We are stipulating two possible ones below:
• 2) A user can simultaneously be connected to both cellular and DOB
technologies. The user can subscribe to a multicast stream on DOB and
later on be directed to subscribe for the same stream on the cellular
technology using multicast or unicast connectivity. This case is not a HO
but rather a receiver selection user case possibly assisted by 802.21
 (Response in next slide)
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802.16 Comments 3/10
 The baseline 802.21 defines handover as “The process by which a mobile
node obtains facilities and preserves traffic flows upon occurrence of a link
switch event. The mechanisms and protocol layers involved in the handover
can vary with the type of the link switch event”
 This use case could be seen as the beginning of a make-before-break
handover. If the DO (downlink only) interface is turned off after the user
has subscribed to the cellular stream, then the handover is completed. In
this case 802.21 Events and Commands can be used to perform such
actions, and the 802.21 baseline already considers such type of handovers.
 Another use case is when a user from the cellular network wants to transfer
to the DO technology and the service has not been started in the DO
technology. In this case 802.21 can be used to notify the DO target network
of the new user so that the service can be started in preparation for the
handover. Such use cases are especially applicable where there is the need
for an optimization of network resource utilization.
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802.16 Comments 4/10
Comments to section 8.1
• PAR language 8.1(a): “Considering the coverage problems of downlinkonly broadcast technologies such as DVB in Europe, the cell-size problems
of IEEE technologies and bandwidth problems of cellular broadcast
technologies, this amendment will improve the user experience during
handovers between IEEE 802.21 supported technologies and other DOB
technologies such as DVB, DMB and MediaFLO”
• Comment 1: HO typically requires uplink communication and NDSF
queries through pull and push. How will DOB/DVB subscriber be able to
query such NDSF server?
 DO technologies rely on a reverse channel of another technology for
providing interactive services. Unidirectional link routing (UDLR) is a
typical example of such cases.
 We foresee relying on the current radio technologies supporting 802.21 as
well as on the L3 transport for supporting two-way MIH communications.
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802.16 Comments 5/10
• PAR language 8.1(a): “Considering the coverage problems of downlinkonly broadcast technologies such as DVB in Europe, the cell-size problems
of IEEE technologies and bandwidth problems of cellular broadcast
technologies, this amendment will improve the user experience during
handovers between IEEE supported technologies and other DOB
technologies such as DVB, DMB and MediaFLO”
• Comment 2: 802.21 is not a DOB technology, the use of the term “other”
needs to be removed. Transition of PoA may be possible but not a transition
of the terminal identity presence in the network.
 Agree: term “other” removed.
 DVB is currently looking at knowing the presence in the network (e.g.
number of listeners) by making use of the interactive channel. In this way,
they could use 802.21 to perform load analysis. In order to determine if
there are enough listeners of a specific service, DO technologies require the
availability of the information regarding the presence of the terminals. If
there are not enough listeners, DO network shifts the service to another
technology where the services are provided either through unicast or
multicast.
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802.16 Comments 6/10
• PAR language 8.1(a): “Considering the coverage problems of downlinkonly broadcast technologies such as DVB in Europe, the cell-size problems
of IEEE technologies and bandwidth problems of cellular broadcast
technologies, this amendment will improve the user experience during
handovers between IEEE 802.21 supported technologies and other DOB
technologies such as DVB, DMB and MediaFLO”
• Comment 3: The most likely Objective of the PAR is to maintain the existing
data packet flows while transitioning a user to a bi-directional technology.
Broadcast is typically an application based procedure that makes
particular content and provides it to an agreed port (socket). The method of
connecting a source socket and transporting its bearer is not within the
realm of an IEEE standard.
 802.21 relies on upper layer protocols for transitioning a specific session
from one technology to another (IP continuity, etc.). The role of 802.21 is
to assist with link layer transition by defining link layer events, providing
network information, etc. The scope of 802.21b would be to provide this
link layer assistance for downlink-only technologies.
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802.16 Comments 7/10
• PAR language 8.1(a): “Considering the coverage problems of downlinkonly broadcast technologies such as DVB in Europe, the cell-size problems
of IEEE technologies and bandwidth problems of cellular broadcast
technologies, this amendment will improve the user experience during
handovers between IEEE 802.21 supported technologies and other DOB
technologies such as DVB, DMB and MediaFLO”
• Comment 4: If the objective is to use another RAT to supply DOB
technology the missing UL channel, the use of 802.21 may not be needed
since the application can invoke a broadcast client to do so without any
change to the MAC or MIH layers. Also, using 802.xx as a bi-directional
interactive channel to support the required DOB signaling is not related to
HO and should not be in scope of 802.21.
 The objective of 802.21b is not to provide the missing UL channel. 802.21
specifies handover related signaling only.
 There are different cases where a HO initiation can take place. In case of a
mobile initiated handover, it is true that a handover can be accomplished
using a technology already supported by IEEE 802.21. However, even in
this case, an interface to the downlink-only technology would be needed to
provide the support for 802.21 services.
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802.16 Comments 8/10
• PAR language 8.1(b): ““Also broadcasters and content providers will be
able to extend their services where DOB technologies may have coverage
problems.”
• Comment 1: Comment 1: How will a DOB provider be able to initiate a HO
and extend its coverage? Say the target is loaded, how will the DOB learn
about it?
• Proposing to delete 8.1(b) from the PAR.
 In the most practical use cases, either the same service provider will
own both the DO network and the IEEE network or the two service
providers will have some kind of a roaming agreement to allow such
types of handover. In both cases, 802.21 provides mechanisms to
learn about the load status of the target network.
 Section 8.1(b) is important, as it mentions that a key market
motivation for 802.21b is to extend coverage of DO network with
IEEE 802 technologies.
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802.16 Comments 9/10
• Comments to Distinct Identity section
• PAR language 8.1(a): “This amendment will facilitate handovers between
DO technologies and IEEE 802.21 technologies.”
• Comment 1: change (a) to: “facilitate handovers between DO technologies
and another RAT that complies with IEEE 802.21 technologies”.
 Agree. Text changed accordingly
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802.16 Comments 10/10
• Comment 2: Inter-DOB handover cannot rely on any uplink signaling. One
can certainly advertise the presence of a neighboring DO system to help the
MS with the scanning process in preparation for the transition and perhaps
also provide a QoS information for a packet flow mapping at the target
DO. However, this type of messaging is typically done above the MAC
layer.
 Although DVB has such information at the MAC layer, 802.21b PAR will
not include handovers between DOBs. This text has been removed from the
PAR.
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802.3 Comments 1/2
• Comment 1. The project claims to be an enhancement of 802.21 protocols,
yet it may be a restriction of 802.21 as described, being a simplex
communication. Simplex communication is not consistent with the 802
Overview and Architecture
 802.21 baseline PAR already includes support for handovers to non-IEEE
802 technologies such as 3GPP and 3GPP2 radio access networks. In this
sense 802.21b is not going beyond the scope of 802.21 nor restricting it.
 Also, DVB and most other downlink-only technologies support two-way
communications e.g. for interactive services. UDLR (Unidirectional Link
Routing) is an example of such two-way communication.
 We foresee relying on the current 802.21-supported interfaces as well as on
the L3 transport for supporting two-way MIH communications related to
downlink-only technologies.
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802.3 Comments 2/2
• Comment 2. Please include within the project documents a commitment to
include a PICS proforma in the initial version of the standard.
 In the base IEEE 802.21 specification, Annex M (PICS proforma) will be
amended to support the new functionality as per ITU-T X.296 and ISO
9646.
 PAR/5C text has been changed accordingly.
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802.11 Comments 1/1
• All acronyms need defining on first usage….see 5.2, 5.4, 5.5 etc.
 PAR/5C text has been corrected accordingly
• If you are handing over from a Broadcast Only to Broadcast Only, how do
you send info uplink?
• See 5.2 Scope and 5.4 Purpose: “may facilitate handovers between DO
technologies. “
 Relevant text has been removed from the PAR/5C.
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